A dagger is essentially a double-edged knife, where the tang is placed along the center line of the blade. The word 'dagger' may have come from Vulgar Latin word 'daca' - a Dacian knife.

Although not technically a dagger, the rondel, a stabbing weapon with triangular or rectangular cross-section, is commonly included in the term.

Some daggers also have weighted blades, and are meant for throwing at enemies. The weighted blade provided momentum and accuracy.

A dagger is more a weapon made for thrusting than a tool for slicing and cutting.

The earliest daggers appear in the Bronze Age, in the 3rd millennium BCE, predating the sword, which essentially developed from oversized daggers. Daggers were important secondary weapons in Europe during the Middle Ages and the renaissance.

A modern version of the dagger is the bayonet, which becomes a spear type weapon when mounted on the barrel of a rifle.